Title: Natural Potassium (K) Isotope Fractionation during Corn Growth and Quantification of K Fertilizer Recovery Efficiency Using Stable K Isotope Labeling
Author: Xin-Yang Chen, Xin-Yuan Zheng*, Brian L. Beard, Matilde Urrutia, Clark M. Johnson, Phillip Barak
Journal: ACS Earth and Space Chemistry
Year of Publication: 2022
Volume: 6
DOI: 10.1021/acsearthspacechem.2c00105
Abstract：An improved understanding of the potassium (K) cycle in soil–plant systems is scientifically and economically significant, but the conventional research based on K concentration measurements has several known limitations. The recent advent of high-precision stable K isotope analysis (reported as δ41K values) can facilitate the use of both stable K isotope labeling and mass-dependent isotopic fractionation in studying the K nutrient cycle, including K fertilizer utilization, and plant–soil interactions. As a proof of concept, we conducted a pot study to quantify the uptake of K fertilizer by corn. Three groups of treatment (50, 100, 200 mg K kg–1 soil) were conducted using soils premixed with different amounts of 41K-labeled fertilizer. A control group used the same soil without fertilizer treatment. Aboveground shoots and soils were sampled and analyzed after ∼6 weeks. The control group showed preferential uptake of light K isotopes by corn with an estimated mass-dependent fractionation of ∼−0.37‰ (±0.23‰) in 41K/39K between the shoot and soil. In fertilized experiments using an enriched 41K tracer, δ41K data unambiguously quantifies fertilizer-derived K in corn shoots, yielding apparent fertilizer recovery efficiency of 59–81%. In comparison, the K concentration-based method underestimated fertilizer utilization at low K treatment and overestimated fertilizer utilization at high K treatment because it cannot distinguish different K sources whose relative contributions to the bioavailable K pool in the soil can vary in response to plant–soil interactions. Our study demonstrates the potential of stable K isotopes in improving the understanding of the K cycle in soil–plant systems.
Key Words: potassium cycle; potassium isotopes; fertilizer; isotope labeling
